COPPER ELECTROPOLISHING IN CONCENTRATED PHOSPHORIC-ACID .2. THEORETICAL INTERPRETATION

A theory for copper electropolishing in concentrated phosphoric acid i s compared to ac-impedance and electrohydrodynamic (EHD)-impedance spe ctra. A water-acceptor mechanism is hypothesized. Agreement between ex periment and theory is good. Curve fits of the EHD-impedance data esti mate that the Schmidt number of the system is Sc approximate to 3 x 10 (6) at room temperature. At temperatures near 90 degrees C, Sc approxi mate to 7 x 10(4). The plausibility of these high values of Sc is disc ussed. These estimates of the Schmidt number are obtained without any assumptions about the bulk concentration of the acceptor. With a known viscosity and diffusion coefficient, the Levich analysis of the varia tion of the limiting current with rotation speed is subsequently used to estimate the bulk concentration of acceptor. The value obtained is in agreement with the known water content in phosphoric acid which ind icates that water is the acceptor species.